882
FXUS65 KBOU 141709
AFDBOU
Area Forecast Discussion
National Weather Service Denver/Boulder CO
1109 AM MDT Wed Mar 14 2018
.UPDATE...
Issued at 1106 AM MDT Wed Mar 14 2018
Updated the forecast for high clouds increasing over the
mountains. Some of this will spread across the plains, but it will
be thinning and shouldn`t have much effect on temperatures. Low
levels upstream remain dry, so only slight chancePoPs for the
mountains through tonight looks appropriate--that may even be too
much.
&&
.SHORT TERM...(Today and tonight)
Issued at 355 AM MDT Wed Mar 14 2018
Before the sunshine and unseasonably warm temperatures
expected today, mtn and high valley areas must contend with
broken to overcast skies generated by a 750-550mb shortwavetrough passing over the area at the moment. NAM 295k-305k
isentropic fields indicate a saturated layer from 10000-15000 ftagl within an area of isentropic upglide. These cloud shield
began showing up on GOES-16 GeoColor visible satellite imagery
over southwest Colorado last evening. Above this layer, the air is
quite dry and subsident. Once this shortwave moves east of the
mtns in the few hours, should see this layer quickly dry out with
the drier air mixing down from aloft. This should result in
plenty of sunshine (at times filtered by passing cirrus) today,
and temperatures on the plains in the mid 60s to lower 70s by
mid-afternoon. FYI, normal high for Denver today is 54 degrees.
High country temperatures should also be quite mild today with the
strong upper ridge passing overhead. Tonight, models show mid-
level moisture moving over western sections of the CWA as
the southwest flow increases with the 500 mbridge axis shifting
east of the mtns. After midnight, isentropic RH fields show cloud
bases lowering to 8000-9000ft asl west of the Continental Divide
by around 06z. Airmass will be quite stable at upper levels, so
any precip will be scanting and confined mainly to the higher
peaks of the Park and Gore ranges after midnight. Otherwise, we`re
in for a mild night with clear to partly cloudy skies, and light
sfc winds east of the mtns.
.LONG TERM...(Thursday through Tuesday)
Issued at 355 AM MDT Wed Mar 14 2018
Main concern will be the ejection and intensification of the
upper low over the central plains late Thursday and early Friday.
Main impacts will be snow and winds in the mountains, and
potential for rain and changing to snow Thursday night on the far
northeast plains. Critical fire weather conditions are also
possible over Lincoln county Thursday afternoon (see fire weather
discussion below).
Computer models are still showing enough variation that
any one solution will have significant impacts on weather over
Eastern Colorado. Currently the NAM is further south and fastest
with intensification of 700mb circulation over far east central
Colorado while the GFS has the low over the Nebraska Panhandle.
Strong upward ascent noted on QG fields with of -20 to
-30mb/hr ascent over plains of northeast Colorado on Thursday
afternoon/evening. Marginal instability may even lead to a few
thunderstorms Thursday afternoon with surface based CAPES up to
500j/kg. Moisture deepens ahead and north of the low Thursday
night and by after midnight temperatures may get cold enough to
turn to snow through Friday am. Could see anywhere from a trace
up to 3 inches over the plains, especially near the Wyoming and
Nebraska border areas.
Behind the upper trof increasing northwest flow aloft will
develop over northern Colorado with favored orographicflow for
snowfall in the mountains along with strong winds. Could see
advisory type amounts for the mountains during the late Thursday
night and Friday morning period but too early to issue any hilites
now. Cross sections show cross barrier flow increasing 40-50kt,
mountain top inversion around 750mb and potential critical layer,
so certainly some gusts up to 60 mph possible over higher
mountains and east slopes. Surface gradient increases to 10-13mb
across the state so certainly strong winds will surface over all
the plains with moderate subsidence in place. Have increased the
winds in all areas late Thursday night and Friday morning. Flow
weakens and dries out by Friday afternoon with diminishing winds
and snow in the mountains. A bit too early, but high wind watches
may be needed over the Front Range in the Thursday night and
Friday am time period.
A brief dry period for Friday night and Saturday morning as weak
ridging aloft moves over Colorado. Short lived though as next
storm system will bring a chance of showers back into the
mountains by Saturday afternoon. More uncertainty in the track of
next system on Sunday with long range models quite varied on
solutions. The GFS is furthest north as it kicks out low way
north through Wyoming and Montana while Canadian solution is
stronger and further south with deepening low over western
Kansas. Confidence is low on any of these scenarios. For now will
have the highest pops again over far northeast Colorado. Drier and
warmer again by the Tuesday-Wednesday time period.
&&
.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1106 AM MDT Wed Mar 14 2018
VFR through tonight. Winds will become more easterly this
afternoon, then back to S/W drainage winds tonight.
&&
.FIRE WEATHER...
Issued at 355 AM MDT Wed Mar 14 2018
Critical weather conditions will increase Thursday afternoon over
Lincoln county (zones 246..247) with lowering humidity and
increasing south to southwest winds. Will be issuing a Fire
weather Watch for Thursday afternoon, ahead of the incoming storm
system. Could be similar conditions on Friday afternoon but will
take it one day at a time.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Thursday afternoon through Thursday
evening for COZ246-247.
&&
$$
UPDATE...Gimmestad
SHORT TERM...Baker
LONG TERM...Entrekin
AVIATION...Gimmestad
FIRE WEATHER...Entrekin